Spray nozzles for high-pressure cleaning applications typically direct a flat spray liquid discharge against a surface to be cleaned. The liquid discharge forcefully impinges against the surface in order to remove dirt or other particles thereon. If uniform cleaning is to take place, it is necessary that the liquid discharging spray have a substantially uniform impingement force for a given area. Heretofore, it has been difficult to achieve such uniformity in the force of the discharging spray particles due to turbulence created within the nozzle body at the required velocity of the liquid spray. Another aim in the development of such cleaning apparatus is to achieve a high cleaning effect with as little as possible consumption of cleaning fluid.